The performance of spectrum analyzers can be degraded by phase noise that is inherent within the spectrum analyzers. For example, phase noise can reduce measurement accuracy of a spectrum analyzer when the phase noise of the spectrum analyzer cannot be isolated from signal measurements that are performed by the spectrum analyzer. Phase noise can also limit measurement sensitivity of the spectrum analyzer. If the phase noise of the spectrum analyzer is sufficiently high relative to the signals being measured, the signals can be masked by the phase noise and go undetected by the spectrum analyzer. Unfortunately, decreasing the phase noise of the spectrum analyzer to improve the measurement accuracy and measurement sensitivity can be costly or difficult to achieve, due to inherent noise within local oscillators, frequency references and other components of the spectrum analyzers that contribute to phase noise. Accordingly, there is motivation to compensate for the effects of phase noise on the measurements acquired by spectrum analyzers.
One phase noise compensation technique is used in the Option 226 Phase Noise Measurement Personality for the AGILENT TECHNOLOGIES, INC. model E4440A PSA series Spectrum Analyzer. This technique includes characterizing the phase noise of the spectrum analyzer by stimulating the spectrum analyzer with a signal having phase noise that is substantially lower than that of the spectrum analyzer, and then measuring the stimulus signal. The resultant phase noise from the measured stimulus signal is subtracted on a linear power scale from subsequent signal measurements that are performed by the spectrum analyzer. This phase noise characterization pertains only to the one particular operating state of the spectrum analyzer at which the stimulus signal is measured. Therefore, in order to compensate for phase noise using this technique, the characterization is typically performed upon each change of the operating state of the spectrum analyzer, which increases measurement set-up time for the spectrum analyzer.